Hair-spring-securing means for instruments



L. BERG May 27, 1930.

HAIR SPRING SECURING MEANS FOR INSTRUMENTS Filed Sept; 17, 1928,jwuanfoz [2 1113 fizzy GUM we :24

,lvllay 27, 193i) ore ETD STATES PATENT OFFICE LCUZEF; BERG, 0F FLINT,MICHIGAN, ASSIGNOR TO A C SPARK PLUG COMPANY, 013 FLINT, MICHIGAN, ACOMPANY OF MICHIGAN EAIR-SPRING-SECURING MEANS FOR INSTRUMENTSApplication filed September 17, 1928. Serial No. 806,424.

This invention relates to measuring instruments and more particularly tothe securing means for the hair spring functioning to restore theindicating means of such instruments to the zero position.

An object of the invention is to provide an improved securing means forthe hair spring to obtain greater uniformity and efficiency.

As another object, the securing means is to such as to avoid twisting ordeformation of the spring at its point of attachment.

Another object of the invention is to pro vide a securing means for thehair sprin whereby the hair spring at its end is hel concentrically inall positions of adjustment.

@ther objects and advantages will be understood from the followingspecification.

The invention is illustrated in the accompanying drawing, in which:

Figure 1 is an enlarged vertical central sectional view of a tachometershowing the hair spring friction adjuster applied;

Figure 2 is a vertical front elevation of the tachometer with the dialremoved to show the adjuster in place;

Figure 3 is an enlarged fragmentary perspective view of the mounting barshowing the hair spring fastened at its end to the friction adjuster;and

Fi ire f is a perspective view of a modified orm.

Referring by reference characters to the drawing, numeral 12 is acup-shaped frame having an apertured stem 11 for the passage of a rotorshaft 10. The rotor shaft is apertured to receive a driving connectionwith a suitable shaft, preferably a flexible shaft, which latter is tobe connected to the rotatable member, the rate of rotation of which isto be measured.

The rotor shaft 10 may have an annular groove 3 to receive a key 5carried bfy the stem 11 to prevent axial movement 0 said shaft 10. Thestem 11 may be provided with a recess 21 containing a suitable wick 23held in position by a cup 251 The purpose of the wick is to carrylubricant for lubricating the engaging surfaces of the stem 11 and shaft10. An outer casing 27 houses the frame 12 and its sleeve 29 issufficiently extended to retain both the key 5 and the cup 25, as shownin Figure 1., This casing 27 is secured to the frame by a plurality ofbolts 31 and nuts 33. The bolts pass through lugs or projectlons 35 and37 formed on the frame 12, as shown in Figure 2. There will be a thirdprojection diametrically opposite lug 37.

pacing means 39 on the bolts between the casing 27 and frame 12,together with a washer 41 and an annular fabric washer 43 between thecasing and the frame serve to secure these parts together in dust-tightrelation.

An annular shoulder 45 in the frame supports a C-shaped magnet 13, themagnet having its interpolar gap adjacent bolt 31 in the projection 35.A temperature compensating plate of known characteristics is placed overthe magnet poles. This is represented by numeral 46. To hold the magnetin position on shoulder 45 and to also hold the compensator on the polesof the magnet clip 46 is formed with an aperture by which it is droppedover bolt 31 and upon the extension 35. The washer 19 and nut 50 clampthe clip in position, the inner end of the clip firmly engaging thecompensator 46.

For the purpose of calibration, a strip of brass or the like 131 may beclamped between parts 46 and 49 and extend substantially radiallyinward. The inner end of this strip of brass may be provided with apiece of magnetic material 133 being held to the brass strip byfastening means 135. By the provision of this calibrating means, thebrass strip may be bent toward or from the plane of the magnet for thepurpose of correcting the active magnetic field. Clips 46 on bolts 31carried by lug 37 and by the diametrically opposite lug are also used.These last-named clips engage the flattened ends 53 of a bridge member55 which is spilt as shown in Figure 2. The ends 53 of this bridge reston the magnet and the clips hold the parts in assembled relation in anobvious manner.

A rotor 9 is secured in any convenient way to the upper end of shaft 10.As illustrated, the end of shaft 10 is reduced to receive on theshoulder so formed the opening within the rotor member 9 and,therea'lter, the en treme end oi the rotor shalt is crimped to hold therotor in position. The rotor is formed with a plurality of radial arms57. Within the openin oil the rotor shaft is a carrier 59 having in itslower end an end thrust bearing 61 and near its upper end a hole jewel63. Secured by threads in the intermediate part of the bridge 55 is asecond bearing carrier having a passage therethrough and a hole jewel65.. The openings in the hole jewels 65 and 63 are in alignment andtogether with the end bearing 61 provide the necessary bearing supportfor a spindle 67 Secured by fastening means 69 to the spindle 67 is ametallic disc i l designed to serve as a drag member and to be rotatedby the eddy currents against the tension of the hair spring 71 securedto the said spindle and to a rotatable adjusting member. Asflit is wellknown in such instruments, the degree of rotation of the drag disc itdepends upon the rate at which rotor 9 travels, cutting as it travelsthe magnetic lines of force between the magnet poles.

A regulator arm 78 rests on bridge and is apertured to rotate about theextended end of carrier 65. This regulator arm extends across the bridgeand on one side is bent down as at to and secured to the lower end ofthe bent-down portion 75 in a manner to be described is the outer end ofspring 71. The other end oi the regulator arm is given a double bend andresiliently engages, by its extended end, forked as at 77, the undersideof the bridge. Rotation of the regulator arm serves to vary the tensionof spring 71.

At the upper end of the spindle is mount ed a part 7 9 carrying anindicating needle 16. The needle moves over a dial plate 19, theperipheral portion of which engages the marginal flanges of casing 27.In practice, there will be a glass cover and a fastening bezel, whichparts are conventional and not illustrated,

The invention is more particularly concerned with the attachment of theouter end of hair spring 71. The down-turned end of the regulator armis, as shown in Figure 3,

. provided with two slits 91 forming three tongues 93. The outermost ofthe tongues 93 are provided with bent portions, the direction of thebend being opposite that of a bend in the intermediate tongue 93. Asshown best in Figure 3, an arc-shaped tubular member 94 is held betweenthe bent portions of the tongues 93 which are sufliciently resilient tohold the member 94 firmly in position. The curvature of tube 94corresponds with that of the hair spring. The end of the hair spring isinserted within the tubular member 94. By this means, the end of thehair spring has the same curvature as that of the major portion of thespring. After insertion in the tube,'the spring may be drawn throughuntilthe desired tension of the coil is had, after which the tube may becrimped to provide a permanent holding means for the end of the spring.After the sprin is firmly secured in the tube, the tube with t e end ofthe spring may be moved relative to the tongues 93, as by slightlypressing the tongues apart. In addition to this provision foradjustment, it will be understood that a fine adjustment may bethereafter made b the rotation of the regulator arm itself a out itspivot.

In the use of hair springs in connection with such instruments, it iscustomary to secure the end of the spring by a tapered pin, after whicha fine ad ustment is bad by manipulating the regulator arm to increaseor decrease the tension of the coil spring, this being accomplished bythe rotation of the regulator arm on its pivot. In so securing the hairspring by wedging with the tapered pin, the concentricity of the coil atthat point is destroyed, because of the flattening effect given to thehair spring at that point, producing a kink therein and more or lessaffooting the uniformity and efiiciency of the coil. By the meansdescribed, this disad vantage has been overcome. The hair spring ismaintained erfectly concentric up to its very end and including itsholding means. The hair spring is therefore not subject to twisting ordeformation at its end when fastens Figure 4 represents a modified andsome what simpler form which may be adopted when desired. In this form,the regulator arm is dispensed with and the hair spring supporting armis formed as an integral part "or the supporting bar 97. The downwardlyextending arm 98 is suitably split and the outer portions are angularlybent to form depressions 99, cutting down the length of these ends andleaving the center portion straight, its end extending further than theothers, this arrangement facilitating the forcing apart of the ends toallow the end of the spring 71 to be pulled through. "With thisarrangement, any adjustment of the hair spring coil may be quickly andeasily made, after which the spring is permanently held in its adjustedposition. This modified form employs a minimum number of parts since theconventional regulator arm and tapered pin are both dispensed with. Itprovides a means of reducing production cost, both in manufacture andassembly.

I claim:

1. In a measuring instrument, a rotary indicating member, a hair springto restore said indicating member to a predetermined position, aretaining means for said spring holding an end of said spring insubstantially concentric relation to the remainder of the spring, saidretainings means including an are shaped tube, the end of the springreceived within said tube.

2. In a measurin instrument, a rotary indicatin member, a air spring torestore said indicat ng member to a redetermined position, a retainingmeans or said spring holding an end of sald spring in substantiallyconcentric relation to the remainder of the spring, said retaining meansincluding an m arc-shaped tube, the end of the s ring received withinsaid tube, said tube eing adjustable circumferentially within theretaining means.

3. In a measuring instrument, an indicating member, a hair sprin torestore said indicating member to a pre etermined position, retainingmeans for said hair spring, said retaining means having at least threeresilient fingers, the outermost fin ers having bent portions, the endof the s rlng being received and held between said ngers, theintermediate finger having a reverse bend, an areshaped tube ositlonedwithin the several bends and hel by the resiliency of said bentportions, the end of the spring being fixedly secured within said tube.

In testimony whereof I aflix m signature LOUI BERG.

